1. Field of the Invention
The present invention relates to an electrode apparatus, such as an intravascular or intracardiac pacemaker or defibrillation electrode of the type having an electrode cable with a jacket of insulation enclosing a first elongated, flexible conductor, connected to a electrode arranged on the electrode cable, and at least a second conductor, connected to a conductive surface arranged on the electrode cable at a distance from the electrode.
2. Description of the Prior Art
Using a bipolar pacemaker electrode apparatus, a heart can be stimulated and cardiac activity sensed with the electrodes arranged on the electrode apparatus. In order to achieve good sensing of cardiac activity, the electrode for this purpose is generally placed at a distance from the stimulation electrode which, in most instances, is arranged at the distal end of the electrode cable. With an implanted intracardiac pacemaker electrode, the stimulation electrode usually presses against the heart wall in the inferior part of the ventricle. If the physician wishes to apply the sensing electrode in the ventricle, atrium or superior vena cava, he or she must select at each implantation occasion, an electrode apparatus for which the distance between the stimulation electrode and the second electrode is such that the latter electrode can be applied at the desired site. Since the size and shape of the heart varies from one patient to another, the physician must have access to a large number of pacemaker electrode apparatuses with different distances between the said electrodes so he or she can select an electrode apparatus in which the distance between the electrodes permits optimal siting of the second electrode. Even with a pacemaker electrode apparatus for intravascular siting, the physician needs to select an electrode cable with an interelectrode distance suitable for the patient in order to achieve optimum sensing and stimulation of the heart.
In U.S. Pat. No. 5,172,694, pacemaker electrode apparatus for intracardiac siting of the type described above is disclosed. By providing the cable of the electrode apparatus with a number of relatively closely spaced consecutive indifferent electrodes, separated from the stimulation electrode, each with its own separate conductor, an attempt was made to reduce the number of electrode apparatuses which have to be stocked at a hospital. When the physician tests these electrodes, individually or in pairs, after the electrode apparatus has been implanted, he or she is able to identify the electrode or electrodes with the best position in the heart or vein and then disconnect the others. The disadvantage of this electrode apparatus is that only a limited number of indifferent electrodes can be arranged on the electrode cable, since the relatively small diameter cable must enclose a corresponding number of conductors. Thus, the portion of the cable length which can be covered with these electrodes is limited, since otherwise the cable's dimensions, flexibility and connections would be adversely affected. Since this length portion is limited, the selectivity available to the physician is correspondingly limited.
U.S. Pat. No. 5,044,375 discloses a defibrillation electrode apparatus for intravascular placement of the aforementioned type. This defibrillation electrode apparatus contains two separately arranged defibrillation electrodes, in addition to a pacemaker stimulation electrode arranged at the distal end of the electrode cable, and a tightly spaced sensing electrode. With this electrode apparatus, the physician is unable to change the distance between the defibrillation electrodes.